They go up when it goes on sale, actually. :D Which is theoretically midnight California time, but in practice is usually 2 or 3 AM California time. Last month the site crashed for several hours immediately thereafter, but the descriptions got posted to alchemylab and bpalanonymous shortly after they went live, so if it goes down for a while again, I'd suggest checking there.

And the BPAL site seems exceptionally prone to caching errors, so force reloads often when you're waiting for the update. :) bpal_excathedra usually has an announcement as soon as it goes live, but they don't post the description there.